arXiv subjects

D. Brown

Publications and source records attributed to D. Brown.

At least 73 records · Page 4Linked to original sources

arXiv2012

A Possible Astronomically Aligned Monolith at Gardom's Edge

A unique triangular shaped monolith located within the Peak District National Park at Gardom's Edge could be intentionally astronomically aligned. It is set within a landscape rich in late Neolithic and Bronze Age remains. We show that the stone is most likely in its original orientation owing to its clear signs of erosion and associated to the time period of the late Neolithic. It is tilted towards South and its North side slopes at an angle equal to the maximum altitude of the Sun at mid-summer. This alignment emphasizes the changing declinations of the Sun during the seasons as well as giving an indication of mid-summers day. This functionality is achieved by an impressive display of light and shadow on the North-facing side of the Monolith. Together with other monuments in the close vicinity the monolith would have represented an ideal marker or social arena for seasonal gatherings for the else dispersed small communities.

physics.hist-ph↗

arXiv2012

Combination of CDF and D0 measurements of the W boson helicity in top quark decays

We report the combination of recent measurements of the helicity of the W boson from top quark decay by the CDF and D0 collaborations, based on data samples corresponding to integrated luminosities of 2.7 - 5.4 fb^-1 of ppbar collisions collected during Run II of the Fermilab Tevatron Collider. Combining measurements that simultaneously determine the fractions of W bosons with longitudinal (f0) and right-handed (f+) helicities, we find f0 = 0.722 \pm 0.081 [\pm 0.062 (stat.) \pm 0.052 (syst.)] and f+ = -0.033 \pm 0.046 [\pm 0.034 (stat.) \pm 0.031 (syst.)]. Combining measurements where one of the helicity fractions is fixed to the value expected in the standard model, we find f0 = 0.682 \pm 0.057 [\pm 0.035 (stat.) \pm 0.046 (syst.)] and f+ = -0.015\pm0.035 [\pm 0.018 (stat.) \pm 0.030 (syst.)]. The results are consistent with standard model expectations.

hep-ex↗

arXiv2012

Search for pair production of the scalar top quark in muon+tau final states

We present a search for the pair production of scalar top quarks ($\tilde{t}_{1}$), the lightest supersymmetric partners of the top quarks, in $p\bar{p}$ collisions at a center-of-mass energy of 1.96 TeV, using data corresponding to an integrated luminosity of {7.3 $fb^{-1}$} collected with the \dzero experiment at the Fermilab Tevatron Collider. Each scalar top quark is assumed to decay into a $b$ quark, a charged lepton, and a scalar neutrino ($\tildeν$). We investigate final states arising from $\tilde{t}_{1} \bar{\tilde{t}_{1}} \rightarrow b\bar{b}μτ\tildeν \tildeν$ and $\tilde{t}_{1} \bar{\tilde{t}_{1}} \rightarrow b\bar{b}ττ\tildeν \tildeν$. With no significant excess of events observed above the background expected from the standard model, we set exclusion limits on this production process in the ($m_{\tilde{t}_{1}}$,$m_{\tildeν}$) plane.

hep-ex↗

arXiv2011

Precise measurement of the top quark mass in the dilepton channel at D0

We measure the top quark mass (mt) in ppbar collisions at a center of mass energy of 1.96 TeV using dilepton ttbar->W+bW-bbar->l+nubl-nubarbbar events, where l denotes an electron, a muon, or a tau that decays leptonically. The data correspond to an integrated luminosity of 5.4 fb-1 collected with the D0 detector at the Fermilab Tevatron Collider. We obtain mt = 174.0 +- 1.8(stat) +- 2.4(syst) GeV, which is in agreement with the current world average mt = 173.3 +- 1.1 GeV. This is currently the most precise measurement of mt in the dilepton channel.

hep-ex↗

arXiv2011

Angular Dependence in Proton-Proton Correlation Functions in Central $^{40}Ca+^{40}Ca$ and $^{48}Ca+^{48}Ca$ Reactions

The angular dependence of proton-proton correlation functions is studied in central $^{40}Ca+^{40}Ca$ and $^{48}Ca+^{48}Ca$ nuclear reactions at E=80 MeV/A. Measurements were performed with the HiRA detector complemented by the 4$π$ Array at NSCL. A striking angular dependence in the laboratory frame is found within p-p correlation functions for both systems that greatly exceeds the measured and expected isospin dependent difference between the neutron-rich and neutron-deficient systems. Sources measured at backward angles reflect the participant zone of the reaction, while much larger sources observed at forward angles reflect the expanding, fragmenting and evaporating projectile remnants. The decrease of the size of the source with increasing momentum is observed at backward angles while a weaker trend in the opposite direction is observed at forward angles. The results are compared to the theoretical calculations using the BUU transport model.

nucl-ex↗

arXiv2011

Peak into the Past - An Archaeo-Astronomy Summer School

Our landscape has been shaped by man throughout the millennia. It still contains many clues to how it was used in the past giving us insights into ancient cultures and their everyday life. Our summer school uses archaeology and astronomy as a focus for effective out-of-classroom learning experiences. It demonstrates how a field trip can be used to its full potential by utilising ancient monuments as outdoor classrooms. This article shows how such a summer school can be embedded into the secondary curriculum; giving advice, example activities, locations to visit, and outlines the impact this work has had.

physics.ed-ph↗

arXiv2010

Archaeo-Astronomy in Society: Supporting Citizenship in Schools Across Europe

The interdisciplinary topic of archaeo-astronomy links science subjects such as astronomy with archaeology and sociology to explore how ancient societies perceived the heavens above. This is achieved by analysing ancient sites such as megalithic monuments (e.g. Stonehenge), since they are the most common remains of these societies and are wide spread in Europe. We discuss how archaeo-astronomy and ancient sites can be transversal to many topics in school. The links to the science curricula in different countries are highlighted. However, especially the subject of citizenship can be supported by exploring the diversity of culture, ideas, and identities including the changing nature of society in the past millennia. We conclude that archaeo-astronomy offers many opportunities for citizenship. Learning more about megalithic monuments in different countries (e.g. England, Portugal, and Germany) supports tolerance and understanding. Furthermore, the distribution of these sites lends itself to explore beyond borders, introduce international networking, and truly develop students into global citizens.

physics.ed-ph↗

arXiv2010

The Archaeo-Astronomy Project -- Supporting the Outdoor Classroom

Field trips and the outdoor classroom are a vital part of many courses at school and FE/HE level. They apply previously obtained skills and knowledge in the field and further deeper learning. However, it would be desirable to teach the material in situ rather than providing a field trip at the end of a course; thereby avoiding referring to the field trip in a few months time where everything will become much clearer. Furthermore, there is clear evidence provided by the National Peak Park Authority on how neglected e.g. the Peak District National Park sites are by Primary and Secondary schools. They quote inaccessibility and other common barriers associated to the outdoor classroom. The archaeo-astronomy project envisages the development of an Elearning environment allowing FE/HE students and pupils (Key Stage 2-4) to experience and explore ancient landscapes e.g. in the Peak District National Park. This project would support the learning experience of students on science and environmental modules. Furthermore, it would allow schools to overcome the initial problems of outdoor classroom. It is a research-based project located at Nottingham Trent University that spans a large age range from secondary school pupils up to undergraduate students. Additionally, it is a collaboration between different departments and highly interdisciplinary including aspects of Astronomy, Physics, Ecology, and Archaeology. A high priority is placed upon the feedback between participants and teachers, especially bridging the gap from HE to secondary schools and colleges. Thereby, students represent role models and support the learning and teaching experience at school level.

physics.ed-ph↗

arXiv2010

Search for pair production of the scalar top quark in the electron-muon final state

We report the result of a search for the pair production of the lightest supersymmetric partner of the top quark ($\tilde{t}_1$) in $p\bar{p}$ collisions at a center-of-mass energy of 1.96 TeV at the Fermilab Tevatron collider corresponding to an integrated luminosity of 5.4 fb$^{-1}$. The scalar top quarks are assumed to decay into a $b$ quark, a charged lepton, and a scalar neutrino ($\tildeν$), and the search is performed in the electron plus muon final state. No significant excess of events above the standard model prediction is detected, and improved exclusion limits at the 95% C.L. are set in the the ($M_{\tilde{t}_1}$,$M_{\tildeν}$) mass plane.

hep-ex↗

arXiv2010

Determination of the width of the top quark

We extract the total width of the top quark, Gamma_t, from the partial decay width Gamma(t -> W b) measured using the t-channel cross section for single top quark production and from the branching fraction B(t -> W b) measured in ttbar events using up to 2.3 fb^-1 of integrated luminosity collected by the D0 Collaboration at the Tevatron ppbar Collider. The result is Gamma_t = 1.99 +0.69 -0.55 GeV, which translates to a top-quark lifetime of tau_t = (3.3 +1.3 -0.9) x 10^-25 s. Assuming a high mass fourth generation b' quark and unitarity of the four-generation quark-mixing matrix, we set the first upper limit on |Vtb'| < 0.63 at 95% C.L.

hep-ex↗

arXiv2010

A Global Citizen of the Skies

Global citizenship plays an important role in today's schools. Many subjects taught in schools have already incorporated such ideas. Science and physics have also followed suit. However, when dealing with astronomy - a topic so seemingly far removed from society - it becomes difficult to imagine any links with global citizenship. At Nottingham Trent University observatory we have developed an activity ideal to transport the idea of global citizenship and deal with common astronomical misconceptions. It incorporates role playing in the inspiring environment of an astronomical observatory. In this activity stellar constellations with their myths and history pose an ideal opportunity to explore global citizenship. Students not only place themselves in someone else's situation, but also compare their different reactions when faced with a common situation. This idea is extended to analyse the change in constellation culture throughout time and the affect politics has had on constellations. In this article we outline the details of this activity and how it deals with common astronomical misconceptions. We also demonstrate its implementation into astronomy taught at schools. First results showing the impact the activity had on the students will also be given.

physics.ed-ph↗

arXiv2008

3He Spin-Dependent Cross Sections and Sum Rules

We present a measurement of the spin-dependent cross sections for the \vec{^3He}(\vec{e},e')X} reaction in the quasielastic and resonance regions at four-momentum transfer 0.1 < Q^2< 0.9 GeV^2. The spin-structure functions have been extracted and used to evaluate the nuclear Burkhardt--Cottingham and extended GDH sum rules for the first time. Impulse approximation and exact three-body Faddeev calculations are also compared to the data in the quasielastic region.

nucl-ex↗

arXiv2007

Impact of Rotation on the Evolution of Low-Mass Stars

High precision photometry and spectroscopy of low-mass stars reveal a variety of properties standard stellar evolution cannot predict. Rotation, an essential ingredient of stellar evolution, is a step towards resolving the discrepancy between model predictions and observations. The first rotating stellar model, continuously tracing a low-mass star from the pre-main sequence onto the horizontal branch, is presented. The predicted luminosity functions of stars of globular clusters and surface rotation velocities on the horizontal branch are discussed.

astro-ph↗

arXiv2007

The Impact of Rotation on the Evolution of Low-Mass Stars

High precision photometry and spectroscopy of low-mass stars reveal a variety of properties standard stellar evolution cannot predict. Rotation, an essential ingredient of stellar evolution, is a step towards resolving the discrepancy between model predictions and observations. The first rotating stellar model, continuously tracing a low-mass star from the pre-main sequence onto the horizontal branch, is presented. The predicted luminosity functions of globular clusters and surface rotation velocities on the horizontal branch are discussed.

astro-ph↗

arXiv2007

Report on the first round of the Mock LISA Data Challenges

The Mock LISA Data Challenges (MLDCs) have the dual purpose of fostering the development of LISA data analysis tools and capabilities, and demonstrating the technical readiness already achieved by the gravitational-wave community in distilling a rich science payoff from the LISA data output. The first round of MLDCs has just been completed: nine data sets containing simulated gravitational wave signals produced either by galactic binaries or massive black hole binaries embedded in simulated LISA instrumental noise were released in June 2006 with deadline for submission of results at the beginning of December 2006. Ten groups have participated in this first round of challenges. Here we describe the challenges, summarise the results, and provide a first critical assessment of the entries.

gr-qc↗

arXiv2007

Detailed comparison of LIGO and Virgo Inspiral Pipelines in Preparation for a Joint Search

Presented in this paper is a detailed and direct comparison of the LIGO and Virgo binary neutron star detection pipelines. In order to test the search programs, numerous inspiral signals were added to 24 hours of simulated detector data. The efficiencies of the different pipelines were tested, and found to be comparable. Parameter estimation routines were also tested. We demonstrate that there are definite benefits to be had if LIGO and Virgo conduct a joint coincident analysis; these advantages include increased detection efficiency and the providing of source sky location information.

gr-qc↗

arXiv2007

A comparison of methods for gravitational wave burst searches from LIGO and Virgo

The search procedure for burst gravitational waves has been studied using 24 hours of simulated data in a network of three interferometers (Hanford 4-km, Livingston 4-km and Virgo 3-km are the example interferometers). Several methods to detect burst events developed in the LIGO Scientific Collaboration (LSC) and Virgo collaboration have been studied and compared. We have performed coincidence analysis of the triggers obtained in the different interferometers with and without simulated signals added to the data. The benefits of having multiple interferometers of similar sensitivity are demonstrated by comparing the detection performance of the joint coincidence analysis with LSC and Virgo only burst searches. Adding Virgo to the LIGO detector network can increase by 50% the detection efficiency for this search. Another advantage of a joint LIGO-Virgo network is the ability to reconstruct the source sky position. The reconstruction accuracy depends on the timing measurement accuracy of the events in each interferometer, and is displayed in this paper with a fixed source position example.

gr-qc↗

arXiv2005

Benefits of joint LIGO -- Virgo coincidence searches for burst and inspiral signals

We examine the benefits of performing a joint LIGO--Virgo search for transient signals. We do this by adding burst and inspiral signals to 24 hours of simulated detector data. We find significant advantages to performing a joint coincidence analysis, above either a LIGO only or Virgo only search. These include an increased detection efficiency, at a fixed false alarm rate, to both burst and inspiral events and an ability to reconstruct the sky location of a signal.

gr-qc↗